1. Field of the Invention
The present invention relates to a terminal electrode forming method for a chip-style electronic component and an apparatus therefor, and more particularly to a terminal electrode forming method for a chip-style electronic component and an apparatus therefor, capable of adapting to miniaturization of the chip-style electronic component, improving the quality of the terminal electrode and adaptable to mass production by executing conductive paste coating etc. while holding the chip-style electronic component by a film coated with an adhesive material.
2. Related Background Art
In general, the terminal electrode formation in a chip-style electronic component means forming a connecting electrode at an end of the chip-style electronic component by coating, drying and sintering paste containing silver, silver-palladium, copper etc. on such end portion, for the purpose of connection with an internal conductor or an internal electrode of the chip-style electronic component. The present invention describes a method for forming a terminal electrode on both ends of a chip-style electronic component such as a ceramic capacitor or a noise filter.
In the conventional terminal electrode forming method for the chip-style electronic component, the chip-style electronic components are held, as shown in FIG. 11, by forming holding holes 51 in silicone rubber 60 and inserting the chip-style electronic components 1, aligned by an insertion guide plate 52, into the holes 51 with inserting pins 53. Such holding method for the chip-style electronic components is however associated with the following drawbacks.
FIGS. 12 and 13 show a state in which the chip-style electronic components 1, inserted and held in the holding holes 51 shown in FIG. 11, are positioned downwards for conductive paste coating, and, in such state, the chip-style electronic components 1 are supported by the elasticity and friction of rubber 50. Thus, at the insertion, the chip-style electronic components are inserted by sliding into the holes 51 of the rubber 50, and, at the holding, they are supported by the elasticity of rubber 50 and the friction of the contact portions. Thus, the chip-style electronic component may not be properly placed at the desired position because sliding and friction, which are mutually contradicting factors, are involved and because of deformation of the rubber 50. Also the mutually contradicting relationship of sliding and friction cannot be controlled because of the minituarization of the chip-style electronic component reduces the contact portion. Also as the holes are formed in the silicone rubber 50, it is necessary to pay attention to the abrasion of the holes 51 and to discard the rubber 50 after certain abrasion.
The feeding mechanism for feeding the chip-style electronic components into the holding holes 51 of silicone rubber 50 is associated with the following drawbacks. For feeding the chip-style electronic components, there is generated employed separation and alignment of the chip-style electronic components by sifting with the insertion guide plate 52 shown in FIG. 11. In this method, as the chip-style electronic components become smaller, the inserting pins 53 also become thinner, thus becoming insufficient in strength and precision. Also the mechanism (jig) becomes inevitably expensive because a high precision is required for the holes of the sifter and those of the holder, and also for the relative positional alignment thereof. In particular, such alignment work is extremely difficult.
Also the conveying mechanism for conveying the chip-style electronic components is associated with the following drawbacks.
The chip-style electronic components having been separated and aligned by the feeding mechanism are held and conveyed by the holes 51 of the silicone rubber 50 formed in the form of a plate or a belt. A plate-shaped holder is conveyed between the process steps either manually or by a robot arm. Manual conveying requires a high labor cost, while robot conveying requires a large and expensive equipment. Also a belt-shaped holder can reduce the labor cost and the floor space required for the equipment, but requires a highly precise conveying mechanism, which inevitably becomes complex and expensive because the alignment is difficult.
Furthermore, the coating surface of the chip-style electronic component has the following difficulties.
Prior to the coating with the conductive paste, the coating faces of the chip-style electronic components have to be aligned with a high precision. Without such alignment work, the dimension B, shown in FIG. 10, of a terminal electrode 2 formed on both ends of the chip-style electronic component 1, namely the length of the electrode in the longitudinal direction of the component, shows a significant fluctuation, and the terminal electrode may not be formed in the worst case.
On the other hand, the plate-shaped holder is suitable for mass production because of the large area thereof, but it is difficult to ensure planarity. Also the belt-shaped holder is formed with a smaller area for a smaller size of production, but it is also difficult to ensure the position because of the reasons explained in relation to the holding method.
Furthermore, the coating mechanism for the conductive paste is associated with the following difficulties.
A coating mechanism shown in FIG. 14A is to form a uniform conductive paste layer 52 on a flat surface a coating bed 60 by means of a squeegee 61, while a coating mechanism shown in FIG. 14B is to form a uniform conductive paste layer 62, by a squeegee 61, on the peripheral surface of a coating roller 66 which is immersed in a lower part thereof in a conductive paste reservoir 65. The terminal electrodes are formed by immersing the end portions of the supported chip-style electronic components in the uniform conductive paste layer 62 formed on such flat surface or on such peripheral surface of the roller.
In case of the plate-shaped holder, the end portions are immersed in the paste layer formed on a flat surface as shown in FIG. 14A. A large area is employed in this method because mass production is intended, and it is difficult to ensure the planarity in such large area.
Also in case of the belt-shaped holder, there is generally employed the coating roller mechanism shown in FIG. 14B, but it is difficult to ensure the precision of the center of the roller and the straightness of the cylindrical surface constituting the roller. Also there is required a high precise parallel relationship between the paste layer and the chip-style electronic components.
Furthermore, the following difficulties are involved in the drying the conductive paste applied on the chip-style electronic components.
The drying of the conductive paste is achieved in an oven using a heater of the electric resistance type, by radiated heat and atmospheric temperature (convection). In order to complete drying by evaporating solvent contained in the paste constituting the terminal electrode, there is required a long time under a high temperature (for example 60 seconds at 180° C.). In order to withstand such high temperature, the conveying mechanism has to be given a heat-resistant property (for example metal belt or heat-resistant conveyor). Consequently the design of the conveying system is limited, and such system inevitably involves complex mechanisms and control with a high cost. Also there is required a large floor space for the equipment. Furthermore, even in case the heat-resistant arrangements are adopted, there still result a change in the conveying position resulting from the thermal dilatation.
Furthermore, a reversing operation executed for forming the terminal electrodes on both ends of the chip-style electronic component is associated with the following difficulties.
In order to form the terminal electrodes on both ends of the chip-style electronic components, it is necessary to position the chip-style electronic components, inserted into the holes 51 of the silicone rubber 50, by pushing them out to the opposite side with the inserting pins 53. In this operation, it is difficult to ensure exact positioning and secure operation because of the reasons explained in relation to the holding method.
Furthermore, the discharging of the chip-style electronic components after the formation of the terminal electrodes, is associated with the following difficulties.
The chip-style electronic components after the formation of the terminal electrodes are finally pushed out from the holes of the silicone rubber for example into a receiving box, but, for this purpose, there is again required a complex mechanism for secure discharge.
Thus, the drawbacks in the conventional terminal electrode forming method can be listed as follows:    1) The terminal electrodes cannot be formed precisely and stably on miniaturized chip-style electronic component;    2) Replacement of the kind of the chip-style electronic components to be processed is time-consuming;    3) There are required high costs for the equipment, consumables and replacement parts;    4) The electrode dimension fluctuates significantly since secure positioning (holding) is not achieved at the electrode forming operation;    5) The relative positional (parallel) relationship between the conductive paste layer and the chip holder is unstable, resulting in a fluctuation in the dimensional precision of the electrode;    6) In the conveying operation in the drying oven, the conveying mechanism exhibits dimensional change and a loss in the holding ability because of the heat; and    7) The long drying time requires a long drying oven, leading to a larger equipment.